[core] Lazy-load esphome.core.config from loader and config

The top-level `import esphome.core.config` in `esphome/loader.py` (used
only to register the "esphome" pseudo-component in `_COMPONENT_CACHE`)
was pulling `esphome.automation` + `esphome.config_validation` eagerly
into every `esphome` CLI invocation, even fast paths like
`esphome version`. Move the cache registration into `_lookup_module`,
triggered on first `get_component("esphome")`.

Also defers the two `esphome.core.config` call sites inside
`esphome/config.py` (CoreFinalValidateStep and validate_config), which
were the other eager entry point.

Local `import esphome.__main__` drops from ~49ms to ~46ms; more
importantly, `esphome.core.config` / `esphome.automation` no longer
appear in the top offenders table, and `esphome.config_validation`
drops from 4.7ms self to 2.0ms self on CI.

esphome/config.py

@@ -25,7 +25,10 @@ from esphome.const import (
     CONF_SUBSTITUTIONS,
 )
 from esphome.core import CORE, DocumentRange, EsphomeError
-import esphome.core.config as core_config
+
+# `esphome.core.config` is imported lazily at its two use sites below.
+# It pulls in `esphome.automation` and `esphome.config_validation`, which
+# dominate `esphome.__main__` startup cost when loaded eagerly here.
 import esphome.final_validate as fv
 from esphome.helpers import indent
 from esphome.loader import ComponentManifest, get_component, get_platform
@@ -968,6 +971,8 @@ class CoreFinalValidateStep(ConfigValidationStep):
         if result.errors:
             return
 
+        import esphome.core.config as core_config
+
         token = fv.full_config.set(result)
         with result.catch_error([CONF_ESPHOME]):
             if CONF_ESPHOME in result:
@@ -1072,6 +1077,8 @@ def validate_config(
         return result
 
     # 2. Load partial core config
+    import esphome.core.config as core_config
+
     result[CONF_ESPHOME] = config[CONF_ESPHOME]
     result.add_output_path([CONF_ESPHOME], CONF_ESPHOME)
     try:

esphome/loader.py

@@ -13,9 +13,13 @@ from typing import Any
 
 from esphome.const import SOURCE_FILE_EXTENSIONS
 from esphome.core import CORE
-import esphome.core.config
 from esphome.types import ConfigType
 
+# `esphome.core.config` is imported lazily in `_lookup_module` when the
+# "esphome" pseudo-component is first resolved. It pulls in
+# `esphome.automation` and `esphome.config_validation`, which together
+# dominate `esphome.__main__` startup cost when loaded eagerly.
+
 _LOGGER = logging.getLogger(__name__)
 
 
@@ -202,6 +206,13 @@ def _lookup_module(domain: str, exception: bool) -> ComponentManifest | None:
     if domain in _COMPONENT_CACHE:
         return _COMPONENT_CACHE[domain]
 
+    if domain == "esphome":
+        import esphome.core.config
+
+        manif = ComponentManifest(esphome.core.config)
+        _COMPONENT_CACHE[domain] = manif
+        return manif
+
     try:
         module = importlib.import_module(f"esphome.components.{domain}")
     except ImportError as e:
@@ -237,7 +248,6 @@ def get_platform(domain: str, platform: str) -> ComponentManifest | None:
 
 _COMPONENT_CACHE: dict[str, ComponentManifest] = {}
 CORE_COMPONENTS_PATH = (Path(__file__).parent / "components").resolve()
-_COMPONENT_CACHE["esphome"] = ComponentManifest(esphome.core.config)
 
 
 def _replace_component_manifest(domain: str, manifest: ComponentManifest) -> None: